Helical twist forces?

Please bear with someone who has not done anything like this before.

The problem I'm contemplating is that the 'scrap' mower I bought has very worn cylinder cutters with no adjustment left. Replacement spools are near £300 each and there's 4 worn ones.

It occurs to me that it should be possible to grind out the old cutter blades and replace them. they are only welded in at one fillet on each support.

To be more specific and longwinded the spools are over 2 foot long (allowing for the end bearings) the cutter section is the central axis with 4 discs evenly mounted..each disc with 6 slots into which the blades sit. And the blades follow a 90 deg spiral from one end to the other over a 22,5in length

The new blades are near enough 1.5in wide and 1/4 in thick. I had in mind to replace them with hot rolled 35x6mm steels (which would have more years of life in them than the machine itself)

There;s obviously going to be a number of ways of shaping the blades. I could lay my hands on a borrowed torch to hot bend but i have no experience of using one and I'm guessing getting an even twist would be a serious skill.

So i was wondering about cold bending since that ought to give an even twist?

What i had in mind is to make up a jig.. essentially a 2 foot square section bar, say 45mm and create a fixed point at one end at the radius needed (about 4 5in guesstimated). I was thinking of making that fixed point out of a sandwich of two bars bolted together since that makes cutting a slot for the new blade-to-be-bent easiest as well as the fixing to the axis bar. For the other end a similar arrangement but turn a bearing surface so that end can rotate - with a much longer lever. (slip a scaffold pole over the end?)

The problems I forsee is that any attempt to clamp this in a vice would likely rip it out of my bench or rip my bench off the floor. I've come up with the idea of clamping the whole arrangment around the base of one of the vertical RSJ's that support a dutch barn and are solidly concreted into the ground.

What remains a bit of a mystery to me is what sort of force and lever length is going to be required to bend and twist this helix - whether that can be done by human power or using my tractors loader bucket?

Indeed whether this is likely to work at all or just a silly idea?

If you aregoing to bend 6 mm x 35 mm, unless your vice is very small, and not well attached to your bench, it should be OK, the tool I use for these bends is a large Cresent spanner, usually the 16" one because its handy, but a 12" one would do(you can be naughty, and use a foot or so of pipe on the spanner if you'r not feeling too strong).

With the old blades, do they file easily? I was just wondering about the durability of mild steel.

Ian S C

Could you not increase the thickness of the fixed blade.? Sounds like a simpler option.

Martin

Or would it not be easier to weld a narrower section onto the underside of the existing blades?

Chris

Build up the worn down blade edges with an arc welder then get them re-ground.

I second Keith Long. These things meet like a pair of scissors so it must be right.

Now finding someone with a cylindrical grinder who won't charge is another matter.

We used to earn beer money in the toolroom sharpening these.

To try and answer in one post..

Bending/twisting the 6mm isn't an issue.. but the helix means one's also bending in the 35mm direction?

I had considered welding a build-up onto the edge. My concerns there are my own welder is tiny (2.5m rods max though i'd love an excuse for a bigger one) and I was also worried about heat distortion. it'd need at least 1/4in build up to be worth it

I'm glad that the idea of welding an extension under the current blades has been brought up.. I also considered that but it was poo-pooed whan i discussed it locally.

Regarding regrinding.. one of the reasons for considerng blade replacement is that if one can get an even twist then it should be possible to set them in fairly close for just a tidy up...?

The blades on there do take a file.

In a worst case I considered following on with a jig to hand dress the new cutters.

Hi Pgk Pgk

Are the cylinders themselves in good enough order to continue using them as is; if you rejigged the knife blades that sit under them. Maybe you could lengthen the slots or pack the blade so it engaged the cylinder more?

Are all four cylinders in need of a refurbishment? I would have thought that some of them would be OK, the same way as the tyres on a car wear at different rates. One or two are normally better than the rest depending on how they were rotated if at all.

Regards
John

If I were you. I'd trade in the lawn for a 'wildlife meadow' and sit back and enjoy it with cool beer

Neil

The bending /twisting is easy enough, getting it right is not easy, I tried it once and gave up. Your welder will be quite capable of depositing a build up on the old blades but you still have the regrind to do, this costs a small fortune, as you will know. I would look at making a new knife blade if possible. Of course when it all finished you will find a mower going for scrap with new drums fitted.

It seems like a lot of work, but why not cut the welds with a thin cutoff disc, pack them out a tad and weld them back in with a spot of weld on each disc. Then cylindrical grind them, or even put between centres on the lathe, mount an angle grinder on the tool post and grind each blade along its spiral ??
BobH

Many thanks for all the suggestions ..food for thought I'll ponder on.

It is cutting at the moment ..although certain types of stalks/clumps get missed and have to be gone over at 90 deg. Supriding really with 4 of the spools's cutters a good few mm from the knife. The blades on the 4 worn spools are virtually down to their supporting discs.

Neil, I have 45 acres of mixed grass/flower meadow - it's nice to have a bit that isn't thigh-deep walking in the summer before hay cutting And the pet sheep would eat all the fruit trees/bushes/veggies if lawnmowing.

I've only been playing with this thing for a few weeks and overall it does make mowing way quicker than the smaller ride-on I have as well as at a faster pace. Suprisingly for an 8-9 foot cut it gets between and under a lot of the trees too and has halved my cutting time - plus cheaper on red than petrol. Having been spoiled like this I'm thinking winter refurb.

Home and Workshop Machinery have a Mower Grinding machine in their MEW ad, as to the price I'll leave you to have a look.

If you are cutting meadow grass why not get a flail mower or topper ? cylinder mowers are for bowling greens ?

These mowers have only 6 blades on the reels, on a bowling green (or golf course) use would use a reel with a lot more blades.

The curtilage was probbaly originally sown with the same flower meadow/grass mix but has been kept mown short for several years and grass has outcompeted the yarrows, yellow rattles and the like.. essentially it's simple lawn.

I do use a topper around field edges and post hay cutting tidy-up, bracken control etc. It doesn't cut anywhere near as close and my one tractor has agri tyres.. which leave serious tracks on the lawns if they aren't bone dry. I'm sure you realise that changing back wheels on a tractor isn't trivial and owning a second tractor with grass tyres is a luxury beyond sense.. let alone the issues of backing in and out of the tree islands, soft fruit, orchards etc. Zero turn mowing is the way.

I;ve been meaning to take some current snaps of the land..perhaps i'll post some here in due course.

To kep the curtilage tidy takes both ride-ons, a push mower and a strimmer.. and around 5 hours work to get around it when this behemoth is in the mix..add another 2-3 hours if just the smaller ride-on. It's usually a couple of hours daily over 3 days and summer time repeat every 5-7 days.

Yes they are 6-bladed spools.

I'd have been inclined to agree the commnet about cylinder mowers for bowling greens etc.. but copared to the rotary ride-on the cylinders give a much more even spray of cuttings (party cos the back deflectors have corroded) compard to the clumpier trails from the husky mulching deck.

An Allen Autoscythe?

Quite apart from the fact it's lawn rather than rough ground... it's has, what?, a 3-4 foot cut width? That'd be a 6-8 mile walk for 3 acres. Would have to make a towable seat.

One would be quite handy for the dodgy hill bits that my tractor skills can;t do except for wrestling it's weight about. feel free to bring one along and chop up the brambles in my steep hilly woody bit..... there's abut 4 acres of closely planted young trees on a 45 deg hillside with waist high throns and brambles - should make a man of you

I put that in pretty much to test people's memory banks etc, it was not meant as a serious suggestion.

I would not even contemplate using one personally because I remember (decades ago) my father wrestling with one on a regular basis cutting the edges of a local cricket ground, not sure about even considering one for a steep hilly bit!

Keeping anything living well behind one was always a wise move as well.

We only have half an acre of what is best described as fairly wild garden, so a small ride on plus a brush cutter does for that.

Edited By V8Eng on 10/06/2015 10:13:06

V8- wish I had an Allen scythe now! You don't have to wrestle with them- you are supposed to start the motor first. I'm in the process of trying to fit a brush cutter onto wheels, my back isn't up to swinging them now. For some reason this is branded Allen.